Hot melt compositions with improved etch resistance

ABSTRACT

Hot melt compositions include non-aromatic cyclic (alkyl)acrylates and low acid number waxes. Upon application of actinic radiation, the hot melt compositions cure to form resists. They may be stripped from substrates with high alkaline strippers. The hot melt compositions may be used in the manufacture of printed circuit boards and photovoltaic devices.

The present application is a continuation application of co-pendingapplication Ser. No. 13/971,537 filed Aug. 20, 2013.

FIELD OF THE INVENTION

The present invention is directed to hot melt compositions with improvedetch resistance. More specifically, the present invention is directed tohot melt compositions with improved etch resistance containingnon-aromatic cyclic (alkyl)acrylates and low acid number waxes.

BACKGROUND OF THE INVENTION

Hot melts are in solid phase at ambient temperatures, but exist inliquid phase at elevated operating temperatures in inkjet printingdevices. At the inkjet operating temperatures droplets of liquid hotmelt are ejected from the printing device and, when the droplets contacta surface of a printing material, they harden to form a predeterminedpattern of droplets.

Hot melts have been employed in direct and transfer printing processes.Hot melts are typically cast into solid sticks and placed into an inkjetprinting device. The temperature of the inkjet device is raised to anoperating temperature where a liquid phase with selective fluidproperties is formed. The hot melt is then held as a liquid at theoperating temperature in a reservoir and printhead of the inkjetprinter. The hot melt in its liquid phase may then be applied in apredetermined pattern onto a substrate. While hot melts have been usedfor some time in the conventional printing industry, the electronicsindustry is beginning to appreciate the potential use of such compoundsto address the problems in the manufacture of electronic devices, suchas in the manufacture of printed circuit boards (PCB s).

PCBs are typically made by complex processes such as with dry filmnegative photoresist processes involving six or more stages. Firstly, adielectric substrate is laminated or coated with copper and the coppersurface is then overlaid with a photoresist layer. A photo-tool isprepared which is a negative of the required electrically conductivecircuitry of the printed circuit. The photo-tool is placed directly overthe photoresist layer to polymerise and harden in those areas exposed tothe UV light to produce a latent image of the required electricallyconductive circuitry in the photoresist layer. The photoresist layer isthen developed to remove the unexposed area of the photoresist. Thischemical treatment is typically mildly alkaline where the photoresistlayer contains free carboxylic groups.

The exposed copper is then selectively removed by chemical etching fromthose areas not protected by the photoresist layers. Finally, theexposed areas of the photoresist layer are removed chemically, forexample using stronger aqueous alkali where the photolayer contains freecarboxylic acid groups.

Although the process is widely used in the manufacture of PCBs it istedious, expensive and wasteful of materials since the photoresist layeris made separately and applied over the total area of thecopper/dielectric substrate laminate. Furthermore, the photo-toolcontaining the negative image of the desired electrically conductivecircuitry is often distanced from the photo-tool layer such thatdiffraction of UV light irradiation occurs and leads to development andpolymerization in areas of the photoresist not directly beneath the UVtransparent areas of the photo-tool. Such problems must be taken intoconsideration when preparing photo-tools and may reduce the density anddefinition of the electrically conductive circuitry. Furthermore, thechemical structure of the photoresist must be carefully controlled sinceits removal both before and after exposure to UV light depends on thealkaline treatment. The density and integrity of the intendedelectrically conductive circuitry can be seriously compromised if eitherthe unexposed photoresist is incompletely removed or if some of theexposed and polymerized photoresist is removed prior to chemicallyetching the copper. Accordingly, there exists significant attraction inapplying photoresist or similar materials to specific areas of acopper/dielectric laminate using inkjet printing technology.

When inkjet printing is done using hot melt inks, the image or negativeimage is made digitally available direct from a computer, the number ofprocess steps is halved, and the need for differential removal of thehot melt ink using mild aqueous alkali is avoided. Also, since there isno photo-tool which is distanced from the hot melt ink layer, there is apotential for improved definition and density of the circuitry. Therealso exists the cost savings in terms of hot melt ink material since thehot melt is only applied to those areas to be protected from chemicaletching.

Substantially complete removal of hot melt materials is highlydesirable. If hot melt residue is left on a substrate after removal, theresidue may compromise further processing of the substrate. For example,hot melt inks may be deposited on a PCB to function as a negative maskfor forming a circuit pattern. Sections of the substrate which are notcovered by the mask are etched away using an etchant and the hot meltink is then stripped. Subsequent steps typically involve one or moremetal plating processes. Any residue remaining on the PCB afterstripping may compromise metal plating resulting in a defectiveelectronic device.

A major problem which often arises during formation of the circuitry isundercutting. This results in defective and inefficient PCBs. Thisproblem is common when the circuits are formed using an etching methodin combination with a mask. Upon application of the etch to theselectively masked substrate the etch may not only remove portions ofthe substrate not covered by the mask but by capillary action seep underthe mask at the interface of the mask and the substrate causing portionsof the substrate covered by the mask to be undesirably etched away. Thisresults in circuitry having irregular widths which results in irregularand non-uniform current flow. In addition, such undercutting may formtributaries which adjoin adjacent current lines resulting in electricalshorts.

Ammoniacal etchant which is a mixture of ammonia and ammonium chloride,is a high alkaline etching solution typically used in the outer layercircuitry fabrication of PCBs as opposed to inner layers. Most alkalineetch baths are designed to work in a pH range of 7.8 to 8.9; however,higher pH is preferred for a faster etch rate to reduce the contact timebetween the etchant and the PCB thus to reduce the opportunity ofspreading of the etchant to other parts of the PCB and attacking theother parts which are sensitive to high pH values. Although most inkjetprintable inner layer etch resist formulations are effective at a low pHrange, inner layers are very sensitive to high pH values of 8.5 orgreater. Etching at high pH can cause chemical attack of some etchresists resulting in an unacceptable large undercut or lifting off oflayers from the substrate caused by a combination of capillary undercutof the etching chemistry and etchants penetrating into the resistcausing swelling and adhesion failure.

As the industry seeks to manufacture electrical devices using thinnerand more delicate circuitry and at the same time increase the pluralityof circuits to increase electrical out-put, the foregoing problemsbecome compounded by difficulty of working with smaller and moredelicate materials. Accordingly, there is a need for a method whichsubstantially reduces or eliminates the problem of undercutting in theformation of electrical circuits and improves stripping of the resistsfrom substrates.

SUMMARY OF THE INVENTION

Hot melt compositions include one or more non-aromatic cyclic(alkyl)acrylates, one or more waxes with an acid number of 0 to 30 mgKOH/g and one or more radical initiators.

Methods include:

-   -   a) providing a hot melt ink composition including one or more        non-aromatic cyclic (alkyl)acrylates, one or more waxes with an        acid number of 0 to 30 mg KOH/g and one or more radical        initiators;    -   b) selectively depositing the hot melt composition on a        substrate;    -   c) applying actinic radiation to the hot melt composition to        cure the hot melt composition;    -   d) etching sections of the substrate not covered with the cured        hot melt composition; and    -   e) removing the cured hot melt composition from the substrate        with a base having a pH of 11 or greater to form a patterned        article.

Methods also include:

-   -   a) providing a hot melt composition including one or more        non-aromatic cyclic (alkyl)acrylates, one or more waxes with an        acid number of 0 to 30 mg KOH/g and one or more radical        initiators;    -   b) selectively depositing the hot melt composition on a        substrate;    -   c) applying actinic radiation to the hot melt composition to        cure the hot melt composition;    -   d) plating metal onto the sections of the substrate not covered        with the cured hot melt composition; and    -   e) removing the cured hot melt composition with a base having a        pH of 11 or greater to form a patterned article.

The hot melt compositions have acid and alkaline resistance up to a pHof less than 11 in contrast to many conventional resists. They adhere ona variety of surfaces with reduced undercut. In addition, the resistsmay be rapidly stripped at pH values of 11 or greater. The hot meltcompositions may be applied to substrates by conventional inkjetapparatus as well as by conventional screen printing methods and byconventional spray apparatus which may have nano- to macro-depositioncapability. The compositions are used as resists. They may be used as aplating resist or as an etch resist.

The hot melt compositions may also be used as an alkaline etch resistfor inner layers of multi-layer substrates. Ammoniacal etchants are verycommon etchants used in etching copper in outer layers during PCBmanufacturing. Ammoniacal etchants are preferred over acidic CuCl₂etchants. Ammoniacal etchants have the advantage of being able to etchexposed copper from the surface of PCBs while not removing tin/leadsolder plating that covers the protected portions of copper circuitry.In addition, acid CuCl₂ etch onsite recovery often involves use ofchlorine gas, a significant health and environmental hazard. Anadvantage of ammoniacal etchants for both outer and inner layerseliminates the need for maintaining two etch modules with different etchchemistries for both inner and outer layer circuitry in PCBmanufacturing.

The compositions and methods may be used in the manufacture ofcomponents of electronic devices, such as PCBs and lead frames,optoelectronic devices, photovoltaic devices, in the metal finishing ofparts and precision tooling. They have good image definition and lowflow due to their phase change nature.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this specification, the following abbreviations havethe following meanings, unless the context indicates otherwise: °C.=degrees Centigrade; g=grams; L=liters; mL=milliliters;cm=centimeters; μ=μm=microns; dm=decimeters; m=meters; mJ=milliJoules;mN=milliNewtons; W=Watts=Amps×Volts; A/dm²=amps per decimeter squared;DI=deionized; wt %=percent by weight; cP=centipoise; UV=ultraviolet;IR=infrared; rpm=revolutions per minute; dpi=drops per inch; 2.54 cm=1inch; PCB=printed circuit board or printed wiring board; KOH=potassiumhydroxide; ASTM=American Standard Testing Method; kV=kilovolts; andpsi=pounds/inch²=0.06805 atmospheres=1.01325×10⁶ dynes/cm²

“Actinic radiation” means electromagnetic radiation that can producephotochemical reactions. “Viscosity”=internal fluid friction or theratio of the shear stress to the rate of shear of a fluid. “Acid valueor acid number”=grams of potassium hydroxide required to neutralize 1 gmof free acid, and to measure the free acid present in a substance.“Moiety” means a specific group of atoms in a molecule. All percentagesare by weight, unless otherwise noted. All numerical ranges areinclusive and combinable in any order, except where it is logical thatsuch numerical ranges are constrained to add up to 100%.

The combination of one or more non-aromatic cyclic (alkyl)acrylatemonomers, one or more waxes having an acid number of 0 to 30 mg KOH/gand one or more radical initiators provides compositions which are hotmelts and when cured may be used as a resist, such as an etch resist ora plating resist, and at the same time are strippable from substratesusing base strippers at pH values of 11 or greater such thatsubstantially all of the cured hot melt composition is removed from thesubstrate. The cured hot melts are resistant to acid etchants, such ashydrofluoric acid, nitric acid, sulfuric acid, phosphoric acid, organicacids, such as carboxylic acids and mixtures thereof, and to industrialetches such as cupric chloride (CuCl₂) and ferric chloride (FeCl₃) andalkaline etchants such as ammoniacal etchants, ammonium hydroxide,ammonium chloride and ammonium sulfate. The compositions are readilystripped from substrates using base strippers such as organic amineswhich include alkanolamines, alkali metal hydroxides, which includepotassium, sodium and mixtures thereof, and alkali carbonates andbicarbonates at pH values of 11 or greater. The net acid number of thecompositions ranges from 0-20 mg KOH/g. Conventional methods known inthe art may be used as sources of actinic radiation to cure thecompositions, such as actinic radiation in the IR, UV and visible rangesas well as X-rays and microwaves as well as other forms of actinicradiation.

The compositions are free of organic solvents as well as water. Thismeans that no additional solvents or water are included in thecompositions and only trace amounts of solvents or water may be presentas impurities or as by-products in the manufacture of various componentsused to make the compositions. Preferably, the compositions are 100 wt %solids. They are low flowing, thus they form printed dots with aspectratios (height to width) in the range of 0.05 to 0.25, or such as from0.08 to 0.18. They also form images having good image definition.

Viscosities of the compositions are such that they may be used with manyconventional inkjet apparatus. Typically, the viscosities of thecompositions range from 4 cPs to 80 cPs from 40° C. to 150° C.Preferably the viscosities range from 8 cPs to 12 cPs from 85° C. to 90°C. Viscosity may be measured by conventional methods but is typicallymeasured using a Brookfield viscometer with a rotating spindle, forexample a number 18 spindle or a CP-42 spindle.

Non-aromatic cyclic (alkyl)acrylates include, but are not limited tomonocyclic, bicyclic, tricyclic and tetracyclic alicyclic(alkyl)acrylates having a bridged skeleton such as adamantine,norbanane, tricyclodecane and tetracyclododecane, and alicyclichydrocarbon groups without a bridged skeleton which include but are notlimited to cycloalkane such as cyclobutane, cyclopentane, cyclohexane,cycloheptane and cyclooctane. Cyclic structures also includenon-aromatic heterocyclic groups such as furan. Such non-aromatic cyclic(alkyl)acrylates have low acid numbers. In general, the acid numbersrange from 0 to 1 KOH/g. T_(g) values may range from 80° C. and greater,preferably from 80° C. to 250° C.

Non-aromatic cyclic (alkyl)acrylate monomers may have the followinggeneral structure:

where R is —(C(R′)₂)_(m)— or —(CH₂)_(p)—O—(CH₂)_(q)— and a carbon oroxygen of R is covalently bonded to a carbon of a ring structure of A,preferably R is —(C(R′)2)_(m)-, R′ is independently hydrogen or(C₁-C₃)alkyl, preferably R′ is hydrogen or methyl, R₁ is hydrogen orlinear or branched (C₁-C₄)alkyl, preferably R₁ is hydrogen or methyl, nis an integer of 1 or 2 where when n is 1 the monomer of structure (I)is a monoacrylate and when n is 2 the monomer structure (I) is adiacrylate, m is an integer of 0 to 2, preferably m is an integer of 0to 1, more preferably m is 1, when m is 0, the oxygen is covalentlybonded to a carbon of a ring structure of A, p is an integer of 0 to 6,preferably p is 0 to 2 and when p is 0, the oxygen is covalently bondedto a carbon of a ring structure of A and q is an integer of 1 to 20,preferably q is 1 to 10, more preferably 1 to 5; and A is a substitutedor unsubstituted monocyclic, bicyclic, tricyclic, tetracyclic carbonring structure having a bridged skeleton, cyclobutane, cyclopentane,cyclohexane, cycloheptane, cyclooctane or a non-aromatic heterocyclicring such as furan. Preferably A is the bridged carbon skeletonstructures adamantine, norbonane, tricyclodecane and tetracyclododecane,more preferably A is norbonane, tricyclodecane and tetracyclododecane,most preferably A is norbonane and tricyclodecane. Substituent groups onthe rings of A include, but are not limited to hydroxyl, oxy (═O), aldo(—CHO), cyano (—CN), halogen such as chlorine, bromine, fluorine andiodine, linear or branched halo(C₁-C₄)alkyl, linear or branchedhydroxy(C₁-C₄)alkyl, linear or branched cyano(C₁-C₄)alkyl, linear orbranched aldo(C₁-C₄)alkyl, linear, branched or cyclic alkyl groupshaving 1-10 carbon atoms, preferably linear or branched (C₁-C₄)alkylsuch as methyl, ethyl, n-propyl, i-propyl, n-butyl, 2-methylpropyl,1-methylpropyl and t-butyl.

Examples of such monomers include the following:

where R and R₁ are defined as above and when the moiety—R—O—C(O)—C(R₁)═CH₂ is joined to either carbon 2 or carbon 3 of the ringhydrogen completes the valence of carbons 2 and 3; R₂, R₃, R₄ and R₅ areindependently hydrogen, halogen, hydroxyl, aldo, cyano, linear orbranched halo(C₁-C₄)alkyl, linear or branched hydroxy(C₁-C₄)alkyl,linear or branched cyano(C₁-C₄)alkyl, linear or branchedaldo(C₁-C₄)alkyl, or linear, branched or cyclic alkyl groups having 1-10carbon atoms, preferably R₂, R₃, R₄ and R₅ are independently hydrogen,hydroxyl, halogen or linear or branched (C₁-C₄)alkyl such as methyl,ethyl, n-propyl, i-propyl, n-butyl, 2-methylpropyl, 1-methylpropyl andt-butyl, more preferably R₂, R₃, R₄ and R₅ are independently hydrogen orlinear or branched (C₁-C₄)alkyl such as methyl, ethyl, n-propyl,i-propyl, n-butyl, 2-methylpropyl, 1-methylpropyl and t-butyl; R″ is themoiety —R—O—C(O)—C(R₁)═CH₂ of structure (II) above, hydroxyl, linear orbranched hydroxyl(C₁-C₄)alky, aldo, aldo(C₁-C₄)alkyl, oxy, or linear orbranched (C₁-C₄)alkyl, preferably R″ is the moiety —R—O—C(O)—C(R₁)═CH₂,hydroxyl, linear or branched hydroxyl(C₁-C₄)alkyl or linear or branched(C₁-C₄)alkyl, x is 0 or 1, when x is 1 and R″ is joined to either carbon5 or carbon 6 by a covalent bond by its carbon or oxygen, hydrogen isbonded to the carbons to complete the valence and when x is 0, hydrogenis joined to carbons 5 and 6 to complete the valence, preferably x is 0.

Examples of monomers also include those having the following generalstructure:

where R, R₁, R₂, R₃, R₄, R₅ and R″ are defined as above and when themoiety —R—O—C(O)—C(R₁)═CH₂ is joined to either carbon 3 or carbon 4 ofthe cyclopentane ring, hydrogen completes the valence of carbons 3 and 4and when R″ is joined to either carbon 8 or carbon 9 by a covalent bond,hydrogen completes the valence of carbons 8 and 9, preferably there isno optional double bond joining carbons 3 and 4 of the cyclopentanering, x is 0 or 1, preferably x is 1 and preferably R″ is the moiety—R—O—C(O)—C(R₁)═CH₂, y is 0 or 1 with the proviso that when y is 0, R″is the moiety —R—O—C(O)—C(R₁)═CH₂, preferably y is 1.

Examples of monomers further include those having the following generalstructure:

where R, R₁, R″ and x are as defined above and when the moiety—R—O—C(O)—C(R₁)═CH₂ is joined to either carbon 8 or carbon 9 of the ringby a covalent bond, hydrogen completes the valence of carbons 8 and 9and when R″ is joined to either carbon 3 or carbon 4 by a covalent bond,hydrogen completes the valence of carbons 3 and 4, preferably R″ ishydroxyl, linear or branched hydroxy(C₁-C₄)alkyl, oxy, aldo, cyano,cyano(C₁-C₄)alkyl or the moiety —R—O—C(O)—C(R₁)═CH₂, more preferably R″is hydroxyl, linear or branched hydroxyl(C₁-C₄)alkyl or oxy.

Examples of additional monomers include those have the following generalstructure:

where R, R₁, R″ and x are defined as above and R₆ is hydrogen, hydroxylor cyano, preferably R₆ is hydrogen or hydroxyl, and when the moiety—R—O—C(O)—C(R₁)═CH₂ is joined to either carbon 1 or carbon 2 of the ringby a covalent bond, hydrogen completes the valence of carbons 1 and 2and when R″ is joined to either carbon 3 or carbon 4, hydrogen completesthe valence of carbons 3 and 4, preferably R″ is oxy, hydroxyl or cyano,more preferably R″ is oxy or hydroxyl and x is 1.

Other examples of monomers include those having the following structure:

where R and R₁ are as defined above and R₇-R₁₇ are independentlyhydrogen, hydroxyl, halogen, linear or branched, substituted orunsubstituted (C₁-C₂₀)alkyl. Substituents include, but are not limitedto hydroxyl, amine, halogen, (alky)acrylate, and linear or branched(C₁-C₄)alkoxy.

The non-aromatic cyclic (alkyl)acrylates may be made by methods known inthe art and literature or may be obtained commercially from varioussources. Examples of commercially available cyclic (alkyl)acrylates aretricyclodecane acrylate, isobornyl cyclohexyl acrylate, isobornylcyclohexyl methacrylate, 3,3,5 trimethylcyclohexyl methacrylate,dicyclopentadienyl methacrylate, tetrahydrofurfuryl acrylate,tetrahydrofurfuryl methacrylate, cyclic trimethylpropanedimethylacrylate, cyclohexane dimethanol dimethacrylate, cyclictrimethylopropane formal acrylate, 2-norbornyl acrylate and SR 833Stricyclodecane dimethanol diacrylate. Many of the commercially availablecyclic (alkyl)acrylates may be obtained from Cray Valley Inc., Akros BVor Cognis Inc. The non-aromatic cyclic (alkyl)acrylates are included inthe hot melt compositions in amounts of 30 wt % and greater, preferably30 wt % to 70 wt % of the composition. More preferably the non-aromaticcyclic (alkyl)acrylates are included in the hot melt compositions inamounts of 40 wt % to 60 wt %.

Waxes which have an acid number of 0 to 30 mg KOH/g include, but are notlimited to waxes of plant origin such as candelilla wax and carnuba wax,petroleum waxes such as paraffin wax or microcrystalline wax, mineralwaxes such as esterified montan waxes, ozokerite, bees wax and ceresinwaxes, synthesized hydrocarbon waxes such as Fischer-Tropsch wax,hydrogenated waxes such as hardened castor oil and fatty acid esters.Such waxes typically contain mainly hydrocarbons or esterified waxes. Ingeneral such waxes may include 40%-80% by weight hydrocarbons oresterified waxes or mixtures thereof. Such waxes are included in the hotmelt compositions in amounts of 5 wt % to 30 wt %, preferably from 5 wt% to 25 wt %. Commercially available examples of such waxes are SP-75from Strahl & Pitsch, Inc. (candelilla wax), SP1026 and SP319 also fromStrahl & Pitsch, Inc. (ceresin waxes), Paraffin Wax 1250 from TheInternational Group, Inc. and LICOWAX® E Flake and LICOLUB® WM 31 bothfrom Clariant (esterified montan waxes).

Radical initiators may be initiators including optional synergists whichare typically used in the trade to initiate polymerization of(alkyl)acrylate functional monomers. The initiator and the synergist,when present may be activated by actinic radiation. Sources of actinicradiation include, but are not limited to, mercury lamps, xenon lamps,carbon arc lamps, tungsten filament lamps, light emitting diodes (LEDs),lasers, electron beam and sunlight. UV radiation is typically used, suchas from medium pressure mercury lamps. Typically, the radical initiatoris a photoinitiator activated by UV light.

Examples of radical initiators and synergists are anthraquinone,substituted anthraquinones such as alkyl and halogen substitutedanthraquinones such as 2-tertiary butyl anthraquinone,1-chloroanthraquinone, p-chloroanthraquinone, 2-methylanthraquinone,2-ethylanthraquinone, octamethyl anthraquinone and 2-amylanthraquinone,optionally substituted polynuclear quinones such as 1,4-naphthaquinone,9,10-phenanthraquinone, 1,2-benzanthraquinone, 2,3-benzanthraquinone,2-methyl-1,4-napththoquinone, 2,3-dichloronaphthaquinone,1,4-dimethylanthraquinone, 2,3-dimethylanthraquinone,2-phenylanthraquinone, 2,3-diphenylanthraquinone,3-chloro-2-methylanthraquinone, retenequinone,7,8,9,10-tetrahydronaphthaanthraquinone,1,2,3,4-tetrahydrobenzanthracene-7,2-dione, acetophenones such asacetaphenone, 2,2-dimethoxy-2-phenyl acetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloro acetophenone, 1-hydroxy cyclohexylphenylketone and2-methyl-1-(4-methylthio)phenyl-2-morpholin-propan-1-one; thioxanthonessuch as 2-methylthioxanthone, 2-decylthioxanthone,2-dodecylthioxanthone, 2-isopropylthioxanthone,2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthoneand 2,4-diisopropylthioxanthone; ketals such as acetophenonedimethylketal and dibenzylketal; benzoins and benzoin alkyl ethers suchas benzoin, benzylbenzoin methyl ether, benzoin isopropyl ether andbenzoin isobutyl ether; azo compounds such as azobisisovaleronitrile;benzophenones such as benzophenone, methylbenzophenone,4,4-dichlorobenzophenone, 4,4-bis-diethyl amino benzophenone, Michler'sketone and xanthone, and mixtures thereof. Examples of commercialinitiators and synergists are Speedcure™ ITX, EHA and 3040, Irgacure™184, 369, 907 and 1850, Daracure™ 1173. Speedcure™, Irgacure™ andDaracure™ are registered trademarks of Lambson Plc and Ciba GmbH,respectively.

Radical initiators are included in sufficient amounts to enable curingof the compositions upon exposure to actinic radiation. Typically, suchradical initiators are included in amounts of 0.1 wt % to 10 wt % of thecomposition, preferably from 1 wt % to 5 wt % of the composition.

Optionally the hot melt compositions can include one or more waxeshaving acid numbers of 100 mg KOH/g or greater. Typically such waxeshave an acid content of 110 mg KOH/g to 250 mg KOH/g. Such waxes are 60%and greater acid functionalized, preferably 70% and greater. Such waxesare included in the hot melt compositions such that the weight ratio ofthe waxes having the acid numbers of 0 to 30 mg KOH/g to the waxeshaving acid numbers of 100 mg KOH/g or greater is from 1:1 to 5:1,preferably from 1:1 to 2:1. Preferably the hot melt compositions includeone or more waxes with an acid number of 100 mg KOH/g or greater. Suchwaxes include, but are not limited to LICOWAX® S, manufactured byClariant GmbH (Germany), with an acid value of 127 to 160 mg KOH/g,LICOWAX® SW with acid values of 115 to 135 mg KOH/g, LICOWAX® UL with anacid value of 100 to 115 mg KOH/g and LICOWAX® X101 with acid values of130 to 150 mg KOH/g. Such waxes are high acid containing montan waxes orn-octacosanoic acid, CH₃—(CH₂)₂₆—COOH, 100% acid functionalized.Carboxylic acid-terminated polyethylene waxes such as myristic acid withacid numbers of 244-248 mg KOH/g, hexadecanoic and palmitic acid withacid numbers of 215-233 mg KOH/g and octadecanoic and stearic acid withacid numbers of 205-210 mg KOH/g may be included.

Optionally the hot melt ink compositions can include one or morenon-cyclic (alkyl)acrylates free of acid groups. Examples of suchacrylate functional monomers free from acid groups are those which arecommercially available under the SARTOMER™, ACTILANE™ and PHOTOMER™trademarks, such as SARTOMER™ 306 tripropylene glycol diacrylate,ACTILANE™ 430 trimethylol propane ethoxylate triacrylate, ACTILANE™ 251a tri-functional acrylate oligomer, PHOTOMER™ 4072 trimethylol propanepropoxylate triacrylate, PHOTOMER™ 5429 a polyester tetra-acrylate andPHOTOMER™ 4039 a phenol ethoxylate monoacrylate. SARTOMER™, ACTILANE™and PHOTOMER™ are trademarks of Cray Valley Inc., Akros BV and CognisInc., respectively. Other examples of monomers are lauryl acrylate,isodecylacrylate, isooctyl acrylate, butyl acrylate, 2-hydroxy ethylacrylate, 2-hydroxy propylacrylate, 2-ethyl hexyl acrylate,1,6-hexanediol diacrylate, neopentyl glycol diacrylate, diethyleneglycol diacrylate, butanediol diacrylate, trimethylolpropanetriacrylate, pentaerythritol triacrylate, 1,3-butyleneglycol diacrylate,1,4-butylene glycol diacrylate, triethylene glycol diacrylate,pentaerythritol tetra acrylate, tripropylene glycol diacrylate andphenoxyethyl acrylate. Such acrylate functional monomers free of acidfunctionality are included in the compositions in amounts of 1 wt % to25 wt %, preferably from 5 wt % to 20 wt %.

Optionally, one or more colorants may be included in the resistcompositions. Such colorants include pigments and dyes includingfluorescing dyes. Colorants may be included in the compositions inconventional amounts to provide a desired color contrast. Suitablepigments include, but are not limited to, titanium dioxide, Prussianblue, cadmium sulfide, iron oxides, vermillion, ultramarine and thechrome pigments, including chromates, molybdates and mixed chromates andsulfates of lead, zinc, barium, calcium and mixtures and modificationsthereof which are commercially available as greenish-yellow to redpigments under the names primrose, lemon, middle orange, scarlet and redchromes.

Suitable dyes include, but are not limited to, azo dyes, metal complexdyes, Naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes,quinoneimine dyes, xanthene dyes, cyanine dyes, quinoline dyes, nitrodyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, penolinedyes, pthalicyanine dyes and leuco dyes. Examples of fluorescent dyesare xanthenes such as rhodamine and fluorescein, bimanes, coumarins suchas umbelliferone, aromatic amines such as dansyl, squarate dyes,benzofurans, cyanines, merocyanines, rare earth chelates and carbozoles.

Additional optional conventional additives include, but are not limitedto, surfactants such as non-ionic, cationic, anionic and amphoteric,slip modifiers, thioxtropic agents, foaming agents, anti-foaming agents,plasticizers, thickeners, binders, antioxidants, photoinitiatorstabilizers, gloss agents, fungicides, bactericides, organic andinorganic filler particles, leveling agents, opacifiers, antistaticagents and metal adhesion agents. Such optional additives may beincluded in conventional amounts.

The hot melt resist compositions may be prepared by any suitable methodknown in the art. The waxes, (alkyl)acrylate monomers and radicalinitiators which are included in the compositions typically are solidsor semi-solids at room temperatures. They may be combined together inany order. They may be heated to soften or liquefy them such that theymay be readily mixed together or with any additional components.Components may be combined in any order in a conventional mixing orhomogenizing apparatus. Temperatures of above 25° C. to 150° C.typically are employed to mix the components. After the components areuniformly mixed the mixture may be cooled to 25° C. or below to form asolid hot melt composition.

Typically the hot melt compositions are applied by inkjet. Inkjetapparatus may digitally store information in its memory for a selectiveresist design to be applied to a substrate. Examples of suitablecomputer programs are standard CAD (computer aided design) programs forgeneration of tooling data. Workers may readily modify the selectivedeposition of the compositions by changing the program digitally storedin the ink jet apparatus. Additionally, registration problems also maybe readily addressed. The inkjet apparatus may be programmed to perceivepotential incorrect alignment between substrates, such as in themanufacture of multi-layer PCBs. When the apparatus sensesmisregistration between boards, the program modifies the inkjetapplication of the resist mask pattern to avoid or correctmisregistration between adjacent boards. The ability to re-design thepattern from board to board reduces the potential for misregistrationbetween the boards, and eliminates the costly and inefficient task ofpreparing multiple fixed phototools. Accordingly, efficiency ofselective deposition of the resist and image formation is improved overmany conventional methods.

There are two major categories of inkjet printing, “Drop-On-Demand”inkjet and “Continuous” inkjet. Using Drop-On-Demand inkjet technologythe resist composition is stored in a reservoir and delivered to anozzle in the print head of the printer. A means exists to force asingle drop of composition out of the nozzle and onto a substrate.Typically this is a piezo electric actuation of a diaphragm within achamber, which “pumps” the droplets out of the nozzles, or a localizedheating of the fluid to increase the pressure within the chamber, thusforcing a droplet to eject.

In “continuous” inkjet printing, a continuous stream of hot melt resistcomposition is delivered to a nozzle in the print head of the printer.Prior to passing out of the nozzle, the pressurized composition streamproceeds through a ceramic crystal subjected to an electric current.This current causes a piezoelectric vibration equal to the frequency ofAC (alternating current) electric current. This vibration, in turn,generates droplets of the composition from the unbroken stream. Thecomposition breaks up into a continuous series of drops, which areequally spaced and of equal size. Surrounding the jet at the point wherethe drops separate from the liquid stream in a charge electrode avoltage is applied between the charge electrode and the drop stream.When the drops break off from the stream, each drop carries a chargeproportional to the applied voltage at the instant at which it breaksoff. By varying the charge electrode voltages at the same rate as dropsare produced every drop may be charged to a predetermined level. Thedrop stream continues its flight and passes between two deflectorplates, which are maintained at a constant potential such as +/−0.1 kVto +/−5 kV, or such as +/−1 kV to +/−3 kV. In the presence of thisfield, a drop is deflected towards one of the plates by an amountproportional to the charge carried. Drops, which are uncharged, areundeflected and collected into a gutter to be recycled to the inknozzle. Drops which are charged and hence deflected impinge on a radiantenergy sensitive material traveling at right angles to the direction ofdrop deflection. By varying the charge on individual drops, a desiredpattern can be applied. Drop sizes may range from 30 μm to 100 μm, orsuch as from 40 μm to 80 μm, or such as from 50 μm to 70 μm in diameter.

The inkjet processes are adaptable to computer control for high-speedapplication of continuously variable data. Inkjet printing methods maybe divided into three general categories: high pressure (10 psi andgreater), low pressure (less than 10 psi) and vacuum techniques. All areknown in the art or described in the literature and can be employed inthe application of the resist compositions to substrates.

In addition to application by inkjet, the hot melt resist compositionsmay be applied by using screen printing and by spray apparatus havingnano- to macro-deposition capability. An example of one type of sprayapparatus which may be used is the M³D® which is available fromOptomec®.

The hot melt resist compositions may be used as etch resists or in thealternative as plating resists. In general, the resist composition isselectively deposited on a substrate followed by curing the resistcomposition with actinic radiation. After curing, the uncovered sectionsof the substrate may be etched to a desired depth or to remove sectionsof the substrate surface to expose underlying layers to form a patternon the substrate. The etchant does not remove the resist from thesubstrate during etching, thus the resist composition functions as anetch resist. The etch resist is then stripped from the substrate leavinga patterned substrate for further processing by conventional methodsknown in the art. In the alternative the uncovered sections of thesubstrate may be plated with a metal to form a pattern on the substrate,thus the resist functions as a plating resist. The plating resist isthen stripped from the substrate leaving a substrate with a metalpattern for further processing by conventional methods known in the art.Stripping is done with a base at pH 11 or higher and at temperaturesfrom 0° C. to 100° C., typically from 40° C. to 60° C. Preferablystripping is done at pH of 11 to 13.

As a variant on the above, the substrate may be selectively coated withthe resist on both sides and exposed to actinic radiation. Etching andplating may then be done on both sides of the substrate simultaneously.

Etching may be done by methods known in the art appropriate to thematerial of which the substrate is composed. Typically, etching is donewith acids, such as hydrofluoric acid, nitric acid, phosphoric acid,hydrochloric acid, organic acids, such as carboxylic acids and mixturesthereof and alkaline etchants such as ammoniacal etchants, ammoniumhydroxide, ammonium chloride and ammonium sulfate. Industrial etchantssuch as cupric chloride (CuCl₂) and ferric chloride (FeCl₃) may be used.Preferably ammoniacal etchants are used when etching multilayer PCBs.Such etches are well known in the art or may be obtained from theliterature.

Etching is typically done at temperatures of 20° C. to 100° C., moretypically from 25° C. to 60° C. Etching includes spraying or dipping theresist coated substrate with the etchant in either a vertical orhorizontal position. Typically, spraying is done when the substrate isin the horizontal position. This allows for quicker removal of theetchant. The speed of etching may be accelerated by agitating theetchant, for example, using sonic agitation or oscillating sprays. Afterthe substrate has been treated with the etchant it is typically rinsedwith water to remove traces of the etchant.

One or more metal layers may be deposited in the pattern formed on thesubstrate. Metals may be deposited electrolessly, electrolytically, byimmersion or light induced plating. Conventional electroless,electrolytic, and immersion baths and methods may be used to depositmetal or metal alloy layers. Many such baths are commercially availableor described in the literature. Metals include, but are not limited to,noble and non-noble metals and their alloys. Examples of suitable noblemetals are gold, silver, platinum, palladium and their alloys. Examplesof suitable non-noble metals are copper, nickel, cobalt, bismuth, zinc,indium, tin and their alloys.

Substrates include, but are not limited to, PCBs, semiconductor wafers,such as for photovoltaics and solar cells, and components foroptoelectronic devices. In general, in the manufacture of PCBs, theresist composition is selectively deposited on a copper clad board andcured using actinic radiation. The sections of the copper clad board notcoated with the resist are etched away. The resist is stripped from theboard leaving a circuit pattern on the board. In another aspect, theresist is selectively deposited on a board made conductive with a metalseed layer using conventional processes and cured using actinicradiation. Sections of the board which are not coated with the resistare plated with a metal or metal alloy. The cured resist is thenstripped from the board leaving a metal pattern on the board.

In general, in the manufacture of a photovoltaic or solar cell, the hotmelt resist is selectively deposited on a front side antireflectionlayer of a doped semiconductor wafer. The antireflection layer may besilicon, silicon nitride Si₃N₄, silicon oxide SiO_(x) or combinationsthereof. Typically, the antireflection layer is Si₃N₄. The semiconductormay be monocrystalline or polycrystalline. The resist is then cured withactinic radiation and sections of the antireflection layer are etchedaway exposing the emitter layer of the doped semiconductor (n+ or n++doped). The cured resist is then stripped and the sections of theemitter layer which are not covered by the antireflective layer areplated with a metal or metal alloy to form a pattern of current tracksand bus bars.

In another aspect the resist may be selectively deposited on a back sideof a doped semiconductor wafer which is coated with a metal, such asaluminum, copper, nickel, silver and gold. The resist is cured usingactinic radiation. Sections of metal which are not covered by the resistare etched away to form a pattern of current tracks for an electrode.

The hot melt compositions have acid and alkaline resistance from pH 1 toa pH of less than 11 in contrast to many conventional resists. Theyadhere on a variety of surfaces with reduced undercut. In addition, theresists may be rapidly stripped at pH values of 11 or greater.

The hot melt compositions may be applied to substrates by conventionalinkjet apparatus as well as by conventional screen printing methods andby conventional spray apparatus which may have nano- to macro-depositioncapability. The compositions are used as resists. They may be used as aplating resist or as an etch resist. The hot melt compositions also maybe used as alkaline etch resists for inner and outer layers ofmulti-layer substrates. The compositions and methods may be used in themanufacture of components of electronic devices, such as PCBs and leadframes, optoelectronic devices, photovoltaic devices, in the metalfinishing of parts and precision tooling. They have good imagedefinition and low flow due to their phase change nature.

The following examples are intended to further illustrate the inventionbut are not intended to limit its scope.

EXAMPLES 1-4

The following inkjet etch resist compositions were prepared:

Formulation 1 2 3 4 Monomers Isobornyl acrylate 48 wt %Dicyclopentadienyl 50 wt %  50 wt % methacrylate Trimethylolpropanetriacrylate  17 wt % Polybutadiene diacrylate 10 wt % Polybutadienedimethacrylate 12 wt % Tricyclodecane dimethanol 60 wt % diacrylateAliphatic urethane acrylate¹  13 wt % Plasticizers Partiallyhydrogenated rosin 20 wt % resin² Hydrogenated rosin resin³ 20 wt %Liquid rosin⁴ 20%  Photoinitiators Isopropyl thixanthone  5 wt %  5 wt %2% 2.5 wt % Hydroxycylohexyll phenyl  5 wt %  5 wt % 3% 2.5 wt % ketoneWaxes Ceresin wax 10 wt % 7.5 wt % Candelilla wax 10 wt % EsterifiedMontan wax 10 wt % Montan wax 7.5 wt % Myristic acid 10% Palmitic acid10 wt % Stearic acid  5 wt % ¹EBECRYL ® 8309 Acrylic Ester from CytecIndustries ²STAYBELITE ® A typical composition and properties: abieticacid <3 wt %, dehydroabietic acid 6-10 wt %, dihydroabietic acid 60-80wt %, tetrahydroabietic acid 5-15 wt %, other resin acids and neutrals10-15 wt %, softening point, Ring & Ball, ° C. = 65-69, acid number158-160 ³Hercolyn Floral AX-E from Pinova solutions inc. ⁴Hercolyn D-Methyl Hydrogenated Rosinate from Pinova solutions inc.

All the formulations were prepared by the same method. The monomers,waxes, plasticizers and the photoinitiators were blended together usinga conventional laboratory blending apparatus at room temperature. Theformulations were 100% solids. The mixtures were then heated in aconventional convection oven within a temperature range of 85° C. to 90°C. The heated resists were then filtered through a conventionallaboratory 1.5μ metal filter while still within the temperature range of85° C. to 90° C. The viscosity of each ink was measured using aBrookfield viscometer with thermosel attachment with a CP-42 spindle.The viscosities of the resists ranged from 8 cPs to 12 cPs. The net acidnumbers for the four inkjet resists were calculated to range from 0-20mg KOH/g.

EXAMPLE 5 Etch Resist for PCB Application

The resist compositions from examples 1-4 were selectively ink jettedfrom a piezoelectric drop-on-demand print head (Spectra™ SE-128) ontofour separate copper clad FR4/glass epoxy panels at a thickness of 15 μmto 30 μm. The temperature during inkjetting was from 85° C. to 95° C.After the resist compositions were selectively applied to theirrespective panels, the compositions were exposed to UV light varyingfrom 150-1000 mJ/cm² using a Fusion D lamp running at 120 W/cm. All theresists cured.

The hardness of each cured resist is tested using the ASTM D3363-05pencil hardness test, 5H being the hardest and 1H being the softest. Thehardness value for each cured resist was measured to be 4H.

Each panel was then passed through a conventional etching modulecontaining a commercial ammonia etchant which was a mixture of 5-15% ofeach of NH₄OH and NH₄Cl at pH 8.9, 52° C. for 5 min. The copper wasetched to a depth of 105 μm. The resist compositions withstood theetching action of the ammoniacal etching solution. There was no visualobservable lifting of panel layers. After etching was completed thepanels were rinsed with water.

Each panel was then dipped in a bath of aqueous stripping solutioncontaining 15% tetramethyl ammonium hydroxide and 5% ammonia solution.The pH ranged from 11 to 12 at 45° C. for one minute to strip the resistfrom the panels leaving a copper circuit pattern on them. The pHdecreased from 12 to 11 as the resist was stripped from the substrateand went into the alkaline solution. Using an optical microscope at 5000power an undercut of 10%-12% was observed as opposed to 20%-25% ofconventional methods. The undercut was measured microscopically by usingthe conventional method of checking the line width of the resist beforeetching and the line width of the copper line after etching.

EXAMPLE 6 Etch Resist for Semiconductor Applications

Solar cells having mono-crystalline or poly-crystalline silicon wafers,a p/n junction and coated with a silicon nitride anti-reflective layeron the front side were provided. Each of the four resist compositions inExamples 1-4 were selectively coated on the anti-reflective layers byinkjet. Each resist was applied to one of the two types of siliconwafers. The resists were then exposed to UV light of 150-1000 mJ/cm² tocure the resists.

Each solar cell was then immersed in a 20% solution of hydrofluoric acidat 30° C., pH=1 for 5 minutes to etch away the uncoated silicon nitrideand expose the n+ doped surface of the silicon. The solar cells werethen rinsed with tap water for 2 minutes and air dried. An opticalmicroscope was used to observe the cured resist on each solar cell.There was no observable loss of cured hot melt on either solar cell. Thecured hot melt appeared to have resisted the acid etch. Each wafer wasthen dipped in a bath of aqueous stripping solution containing 15%tetramethyl ammonium hydroxide and 5% ammonia solution at 45° C., forone minute to strip the resist from the solar cells leaving a siliconnitride pattern on the them. Using an optical microscope at 5000 power a10%-12% undercut was observed as opposed to the typical conventionalundercut of 15% or more.

EXAMPLE 7 Plating Resist for PCB Applications

The resist compositions from examples 1-4 were selectively jetted from apiezoelectric drop-on-demand print head (Spectra SE-128) onto fourseparate freshly copper plated acid test coupon panels at a thickness of15 μm. The temperature during inkjetting varied from 85° C. to 90° C.After the resist compositions were selectively applied to theirrespective panels, the compositions were exposed to UV light varyingfrom 150-1000 mJ/cm² using a Fusion D lamp running at 120 W/cm. All ofthe resists cured.

The hardness of each cured resist was tested using the ASTM D3363-05pencil hardness test. The hardness value was 4H for each sample.

The samples were immersed in an ambient 10% sulfuric acid pre-dip fortwo minutes and plated in a RONASTAN™ EC Acid Tin plating bath at 23° C.at a current density of 12 A/dm² for 8 and 10 minute dwell times. Tinmetal was deposited in sections not coated with the resists. Tindeposition was done until the tin deposit was 0.25 μm to 2 μm. Thefinished coupons were rinsed and air dried with compressed air.

Each panel was then dipped in a bath of aqueous stripping solution of15% tetramethyl ammonium hydroxide and 5% ammonia at 45° C., for oneminute to strip the resist from the panels leaving a copper circuitpattern underneath a tin plated layer.

EXAMPLE 8 Plating Resist for Semiconductor Applications

Solar cells having of mono-crystalline or poly-crystalline siliconwafers, a p/n junction and coated with a silicon nitride anti-reflectivelayer on the front side were provided. Each of the four resistcompositions in Examples 1-4 were coated on the anti-reflective layer ofthe two types of silicon wafers. The resists were then cured by exposingthe front of the solar cells to UV light at 150-1000 mJ/cm².

Each solar cell was then immersed in a 20% solution of hydrofluoric acidat 30° C., pH=1 for 5 minutes to etch away the uncoated silicon nitrideand expose the n+ doped surface of the silicon. The solar cells werethen rinsed with tap water for 2 minutes and air dried. An opticalmicroscope was used to observe the cured hot melt on each solar cell.There was no observable loss of cured hot melt on either solar cell. Thecured hot melt appeared to have resisted the acid etch.

Each solar cell was then immersed into a bath of ENLIGHT™ 620 SilverElectrolyte solution (available from Dow Electronic Materials). Thesolar cells were connected to a rectifier and the counter electrode wasa soluble silver electrode. Light from a fluorescent/LED lamp 8-12 W wasapplied to the front side of each solar cell and a current density of0.5 A/dm² was applied. The silver electrolyte was maintained at atemperature of 40° C. and silver plating was done for 15 minutes.

After plating was completed each solar cell was placed under the opticalmicroscope. All of the exposed n+ doped silicon sections were platedwith silver. The cured hot melt appeared intact. Each wafer is thendipped in a bath of aqueous stripping solution of 15% tetramethylammonium hydroxide and 5% ammonia solution at 45° C., for one minute tostrip the resist from the solar cells leaving an etched pattern. Theundercut for the mono-crystalline solar cell was 12% and the undercutfor the multi-crystalline was 10%. This was below the typical undercutfor wafers of 15% or more.

EXAMPLE 9 Comparative

FR4/glass-epoxy copper coated substrates were selectively coated withhot melt compositions as in the Table above except the cyclic acyrlateswere replaced with one of the following low volatile acrylates:propoxylated neopentyl glycol diacrylate for isobornyl acrylate,dipropylene glycol diacrylate and tripropylene glycol diacrylate fordicyclopentadienyl methacrylate, and propoxyethyl methacrylate fortricyclodecane dimethanol diacrylate. The amounts of each replacementacrylate were the amounts of the cyclic acrylate used in theformulations of the Table. A plurality of selectively applied linesusing the inkjet printer was jetted onto each substrate. The resistswere applied to the substrate at nozzle temperatures of around 85°C.-90° C. The resists were cured using UV light at 150-1000 mJ/cm².

Each substrate was then sprayed with 15% ammonia and 5% cupric chlorideetching solution at pH 8.9 at 52° C. Each substrate was exposed to theetching solution for 1 minute then the substrates were rinsed with DIwater for two minutes. Examination of each substrate with an opticalmicroscope indicated that substantially all of the cured resists wereremoved and the portions of the copper covered by the resists were alsoetched. This indicated that resists which excluded the alicyclicacrylates had decreased alkaline resistance.

What is claimed is:
 1. A hot melt composition comprising one or morenon-aromatic cyclic (alkyl)acrylates in amounts of 30 wt % to 70 wt %,one or more waxes comprising an acid number of 0 to 30 mg KOH/g and oneor more radical initiators, the hot melt composition is 100% solids. 2.The hot melt composition of claim 1, further comprising one or morewaxes comprising an acid number of 100 mg KOH/g or greater wherein aweight ratio of the one or more waxes comprising an acid number of 0 to30 mg KOH/g to the one or more waxes comprising an acid number of 100 mgKOH/g is 1:1 to 5:1.
 3. The hot melt composition of claim 2, wherein theweight ratio is 1:1 to 2:1.
 4. The hot melt composition of claim 1,further comprising one or more non-cyclic (alkyl)acrylates free of acidgroups.
 5. The hot melt composition of claim 1, wherein the one or morenon-aromatic cyclic (alkyl)acrylates are in amounts 40 wt % to 6 wt %.6. The hot melt composition of claim 1, wherein the one or morenon-aromatic cyclic (alkyl)acrylates are chosen from tricyclodecaneacrylate, isobornyl cyclohexyl acrylate, isobornyl cyclohexylmethacrylate, 3,3,5 trimethylcyclohexyl methacrylate, dicyclopentadienylmethacrylate, tetrahydrofurfuryf acrylate, tetrahydrofurfurylmethacrylate, cyclic trimethylpropane dimethylacrylate, cyclohexanedimethanol dimethacrylate, cyclic trimethylopropane formal acrylate,2-norbornyl acrylate and tricyclodecane dimethanol diacrylate.
 7. Thehot melt composition of claim 1, wherein a net acid number of the hotmelt composition is 0-20 mg KOH/g.